Injection pump

An injection pump is a metering pump for high pressure and is a component of the fuel injection in internal combustion engines. The injection pump per stroke is a defined amount of fuel at the necessary pressure willing to pump fuel through the injector into the combustion chamber or the intake manifold. It is required when diesel engines for injecting the diesel fuel and more and more replaced by common-rail systems since the turn of the millennium. Since the thirties injection instead of carburetors were also used in gasoline engines.

Even with liquid fuels gas turbines and rockets require defined amounts of fuel with partially high pressure. The pumps used therein are not referred to as injection pumps.

Scope

Injection pumps are widely used in diesel engines. They are required for the high-pressure injection of fuel into the combustion chamber. Because of the high pressures, the compressibility of the fuel is no longer negligible, as the reversible upon pressurization longitudinal and lateral expansions of the metal pipes, so that the design of the diesel fuel injection system necessarily the oscillations of the fuel column are to be considered in the injection lines. For this reason, the injection lines of the sake of simplicity, for each cylinder are performed in the same length.

Since the early 1950s were also injection for gasoline engines in motor vehicles in use. The first production car with mechanical fuel injection were the Gutbrod Superior and Goliath GP 700 E (1951 ), and later the Mercedes- Benz 300 SL (1954). Since the seventies, electronically controlled injection systems prevail with electrically driven pump where the fuel injection pressure on variable or variable injection duration is metered. Also because of the exhaust laws of many states, they are built with the most modern passenger car gasoline engines.

Function

The task of the injection pump it is,

• Fuel to dose accurately,
• To the right time, and
• About the correct period

Inject.

In addition, control of the injection pump to adjust the fuel delivery in dependence on the engine speed and operating temperature.

Thus, the fuel injection pump as a unit a number of tasks. It is used for a pure fuel transport from the fuel tank to the engine. This latter has a fuel pump, which is usually the speed runs synchronously to the engine. In fuel pumps without volume control thus follows the quantity of fuel delivered to the engine speed. Since the delivered amount is higher than the actual demand, the surplus on a separate return line is returned to the fuel tank. This also allows an excessive local heating of in parts of the fuel injection pump can be reduced as a result of the inevitable friction. In addition, the fuel filter and the fuel tank is heated by the return pipe.

Furthermore, the pump has at least one further, controlled high-pressure pump, which determines both the timing and the amount of actual fuel injection.

In the above method, various pumping systems for the construction of the injection pressures are used:

• For engines with prechamber or swirl chamber injection Single injection pump
• Distributor injection pump, or
• Series injection pump

• For engines with direct injection Single injection pump
• Series injection pump
• Distributor injection pump

Basic information on the structure

Injection pumps are discontinuous promotional piston engines. The pressure build-up is done by a piston linear movement. The energy for the printing operation is in rotation, taken from a motor-driven, tightly coupled to the crankshaft camshaft gear ratio and transferred to the piston or pistons. The implementation of the rotation to the translation of the piston does not happen via a crank mechanism (via the connecting rod and piston pin ) out for round -trip movement, but a direct pressure generation under friction. Thus, the kinematics of particular line injection is similar to the valve train and camshaft via tappets on the intake and exhaust valves of a reciprocating engine.

Types of injection pumps for diesel engines

The following types of piston plays a central role as pumping and metering.

Line injection pump

In a series injection pump, the individual to the respective cylinders of the associated pump elements are combined in a housing or are arranged as individual modular pump side by side on a drive shaft. The line injection pump has regulations for the speed, injection quantity and the injection timing ( timing device ). The individual pump elements are built as reciprocating pumps and bore and stroke ( design and operational reasons ) can not be changed. In order to achieve a variable dosage, the pistons are made about its symmetry axis for rotation. They can be simultaneously rotated by a rack during operation. The cylinder casing of the pump piston is provided with an arcuate milled recess, which - depending on the rotation position of the piston - the supply bore in the pump cylinder wall passes over and closes. The closure of the inlet bore is the start of delivery of the pump element. A modification of the in-line injection pump is a radial piston pump. The line injection pump requires external lubrication, either by connection to the engine oil circuit or a separate oil sump. Line injection are due to the separation of lubrication and pumped fuel distributor injection as compared to more robust. Diesel injection systems with in-line injection pumps have been replaced today by the majority of common rail, pump-line- nozzle or pump - nozzle systems.

Distributor injection pump

The distributor injection pump is driven by a shaft from the motor and with it the built- in pump housing pre-supply pump, usually a vane pump. This draws in the fuel from the fuel tank and conveys it into the pump interior. The fuel pressure inside the fuel injection pump is regulated by a pressure control valve. Thereafter, the high-pressure part of the pump, which generates the injection pressure follows.

In this case, there is only one pumping element, which supplies the individual cylinders by means of a downstream distributor. The number of strokes of the pump element is calculated from the half engine speed, multiplied by the number of cylinders (with a four stroke engine ). Also in this case, the injection quantity and injection timing are controlled, the controlled variables are the load and speed. A distributor injection pump is controlled much cheaper in production and more accurate compared to the in-line injection pump. The outer dimensions are more compact.

It requires no supply of lubricating oil through the engine oil. The moving parts of the distributor injection pump are lubricated by the fuel and therefore must have the lubricating properties. The distributor injection pump is more sensitive to differences in viscosity of various fuels at various temperatures, such as Vegetable oil and diesel fuel or biodiesel ( summer and winter). The pump piston is due to the significantly higher number of strokes mechanically loaded higher than the pumping elements in the series injection pump. In case of failure on the distributor pump piston diesel engine inoperative while in -line injection pumps to continue the journey with a single defective pump element on the remaining cylinders under certain circumstances is still possible.

Distributor fuel injection pumps may be implemented as an axial or radial piston pump. The latter can produce maximum pressures up to 1950 bar. Usually produce a discharge pressure of 3 to 8 bar, the. To max Is limited to 12 bar. An EDC electronic diesel control is possible, on the one hand enables a higher accuracy of the rules, on the other hand operating the motor without power impossible. The last distributor pumps had integrated pump control devices, some of which contained the functions of an EDC.

The drive shaft and the camshaft speed is in the lifting piston pump and distributor piston into rotary motion. The cam plate is provided with cams, which slide on the rollers of the roller ring. The distributor piston connected to the lifting thereby carries out rotary-lift movement. As soon as the supply passage is closed to the high pressure chamber, the fuel is compressed by the reciprocating motion. By the further rotation of the piston, a discharge hole is opened to an injection nozzle and the fuel is pressed by a pressure valve to the nozzle, and it is for injection into the combustion chamber.

With the radial piston pump, the pressure is no longer generated by a stroke movement of the distributor plunger, but by radial pumping elements, which are actuated by the rotational motion of the distributor piston. This design is more complex than an axial piston pump, but allows higher injection pressures.

Since the early 2000s the diesel injections have been largely replaced with distributor injection of common rail systems in passenger car construction. The Volkswagen Group used from the late 1990s pump nozzle (PD ) injections in his car diesel engines. Since PD systems due to their rapid pressure build-up have a little cultured engine running and also compared with the cross-vendor applied common-rail systems have higher, as -applied only in the VW group niche product irreducible production costs, the VW group has the end of the 2000s his diesel engines also converted to the common-rail technology.

Single -plunger pump

This corresponds to the in-line injection pump, each cylinder is controlled by a separate pump; the machine is driven by the camshaft.

Especially for truck diesel engines with camshaft in such pumps are also known as plug-in pumps. These are used, for example, Mercedes- Benz engines from the 900 series or 500 with the plug-in pump pressures up to 1850 bar and double injection can be achieved.

Pump nozzle

In the pump-nozzle system, the single -plunger pump is combined with the injector. This reduces the disturbing influence of fuel pressure lines to the system. The control of the pump element was used to mechanically, nowadays, the injection period is controlled by a piezoelectric or solenoid valve. These valves connect to state pressure channel and return open. Characterized the pressure collapses, and the injection nozzle closes., The injection pressure is, however, strongly dependent on the speed of the driving cam and not adjustable.

High pressure pump for common rail

The high-pressure pump which generates the high-pressure diesel in the common rail systems is seen just an injection pump. The Common Rail pump is only as to the pressure regulated, but not for quantity and timing rules of the cylinder injection as with other injection systems; these control functions are performed outside of the pump in an electronic control means and the controlled of their injectors. To ensure the deliverables pressure and the required flow rate, various methods are used. So either is a pressure control, used a system of the supplied volume or a combination of both types. Because common rail pumps with pressures up to 2,000 bar work (in development after January 2006: 2,400 bar), the mechanical forces inside the pump are high. There are also ever-increasing fuel temperatures that reduce the lubricity of diesel fuel. As a result mainly of cost reasons, the pumps are lubricated by the diesel fuel itself, the bearings and sliding surfaces are tribological heavy burden because of the limited lubricity and are prevented by considerable expenditure on food.